Mycology is the study of fungi, of which there are over 100,000 known species but only about 200 that can cause human disease. Fungi have cell walls containing chitin and reproduce both sexually and asexually. Common fungal infections include ringworm, athlete's foot, and nail fungus caused by dermatophytic fungi. Systemic fungal infections occur when fungi enter the bloodstream, often through the lungs, and can spread throughout the body. Opportunistic fungal infections mainly affect immunocompromised individuals. Aspergillosis is a common fungal pneumonia caused by inhaling Aspergillus spores. Pneumocystis pneumonia is seen primarily in AIDS patients. Candid

1. Mycology and Fungal Pathogens

2. Mycology
• Study of fungi
– Greater than 100,000 fungal species
• Only ~200 human/animal pathogen
• FUNGI
– Eukaryotes: Yeasts and molds
– Cell wall – Chitin
– Cell membrane - ergosterol
– Chemoheterotrophs
• Require organic compounds for carbon and energy
– Food industry: bread, alcohol, edible fungi (mushrooms), cheeses
– Some are deadly
– Adapted to environments hostile to bacteria
• pH 5
• High osmotic pressure
• Low moisture
• Complex carbohydrates (ex. Lignin from wood)
• Less nitrogen

3. Yeast
• Unicellular fungi
– Spherical
– Facultative anaerobe
– Reproduce
• budding or fission
• Budding Yeast
– Ex. Saccharomyces
– Uneven division
• Bud forms on outer surface
• Parent nucleus divides
• One nucleus migrates into bud
• Cell wall forms, bud breaks away
• Fission Yeast
– Ex. Shizosaccharomyces
– Binary fission  identical daughter cells

4. Molds and Fleshy Fungi
• Multicellular
• Aerobic
• Composed of hyphae
– Long filaments of cells joined together
• Grow by elongating at ends
• Fragments break off to form new hyphae
Hyphae:
• Vegetative
– Part that absorbs nutrients
• Aerial
– Projects above medium
– Bears reproductive spores

5. Fungal Reproduction
Molds (multicellular fungi)
• Asexual reproduction
– Fragmentation
• Hyphae break off to form new molds
– Spores
• Asexual spores
– Form by mitosis, detach from parent, germinate to form new hyphae identical
to parent
• Sexual reproduction
– Sexual spores
• Formed by fusion of nuclei from two opposing mating strains
• Detach from parent structure
• Germinate into new mold
• Contain genes from both parent fungi

6. Asexual Spores
• Examination of spores aid clinical identification
of fungal infection
• Two Types
– Sporanigospore
• Formed in sac (sporangium) at end of aerial hyphae
(sporangiophore)
• Ex. Rhizopus
Hundreds of spores in a single sac

7. Asexual Spores: Condiospore
• Also called Conidia (“dust”: detach easily and
float like dust!)
• Not enclosed in a sac
• Seen as chains at end of conidiophore
• Ex. Aspergillus

8. Other Conidia: Arthoconidia and
Blastoconidia
Arthoconidia = conidiospores
formed by fragmentation of a
hypha into single cells
Ex) Coccidioides immitis
Blastoconidia = conidiospores
formed by buds coming off the
parent cell
Ex) yeasts like Candida albicans
Other fungi: Cryptococcus (yeast
stage)

9. Spore Formation
• Hyphae forms conidia (or sporangia)
• Spores disseminate in air
• Inhalation  irritants  allergens
– also spores in respiratory system  source of
infection

10. Fungal Toxins
• Some fungi secrete toxins
– Muscarin: Hallucinogenic
– Phalloidin: irreversible damage to liver cells
– Amanitin: inhibits RNA polymerase II activity
– Aflatoxin (Aspergillus flavus)
• Liver damage
– Ergot (Claviceps purpurea)
• Gangrene, convulsions,
hallucinations (LSD)
Deathcap (Amanita phalloides)

11. Mycoses
• Fungal Infections
– Usually chronic, fungi grow slowly
– Treatment difficult
• Fungi are eukaryotes
• Antifungals can affect human cells
– Serious kidney, liver failure
• Types of Mycoses
– Cutaneous
– Subcutaneous
– Systemic
– Opportunistic

12. Cutaneous Mycoses
• Fungal infection of skin, hair, nails
• Dermatophytes
– Cause only cutaneous infections
– Secrete keratinase to degrade keratin
Trichophyton, Epidermophyton, Microsporum
Need to remember those names and what they cause

13. Tinea pedis: Athlete’s Foot
• Caused by Trichophyton
– Multicellular hyphae with asexual spores (arthroconidia)
• Results in scaling, flaking, itching of feet
• Transmission
• Contagious – can be spread through contact
• Reservoirs = warm, damp areas
• Prevention
• Keep skin clean and dry
• Wear sandals in community pools and showers
• Wash hands after touching other people/
animals that may carry fungal infections
• Treatment
• Topical antifungals
Trichophyton rubrum
Do not need to remember treatments unless told

14. Tinea capitis (ringworm of scalp)
• Caused by Microsporum genus
• Grows as multicellular hyphae
• asexual spores (conidiospores)
• Found in soil and on animals
• Results in inflammation, scarring,
permanent hair loss
• Transmission = touching infected
human or animal, touching infected objects
• Treatment = terbinafine hydrochloride (lamisil) ingestion

15. Subcutaneous Mycoses
• Infection beneath the skin
• More dangerous than cutaneous
• Usually from soil dwellers invading
puncture wounds
• Ex) Sporotrichosis: Sporothrix schenkii
• Most common subcutaneous mycosis
• Dimorphic: 25oC – hyphae, spores
• 37oC – yeastlike, budding
• Transmission = handling of soil or plant material
• Symptoms = small ulcer where it entered
• Spread along lymph vessels creating more ulcers
• Treatment = potassium iodide (ingestion), itraconazole

16. Systemic Mycoses
• Fungal infection affecting internal organs
• Soil dwelling fungi
• Initiated by inhaling spores
– Infection in lungs
– Spreads to other parts of body
Histoplasmosis:
• Histoplasma capsulatum
• Dimorphic = filamentous in soil,
yeast-like morphology in tissue
• lives, multiplies in macrophages
• Symptoms: mainly mild respiratory infection
• Treatment: if severe, intravenous Itraconazole

17. Histoplasmosis: geographic distribution
Areas of moist soils are good for H. capsulatum growth
 more airborne spores

18. Systemic mycoses: Coccidioidomycosis
• Valley Fever
• Coccidiodes immitis
• Dry, alkaline soils of American SW,
S. America and Mexico
• Dimorphic = filamentous in soil;
thick-walled spherule filled with spores in tissue
• Symptoms = Chest pain, fever, coughing, weight loss
• Diagnosis = Identification of spherules in tissue/fluids
• Treatment = Most recover without treatment

19. Systemic Opportunistic Mycoses
• Opportunistic mycoses
– Fungal infection occuring in immunocompromised
human/animal
• Ex) Pneumocystis pneumonia
• Pneumocystis jirovecii
• Few or no symptoms in healthy lungs
• Symptoms in immune compromised
 Primary indicator of AIDS
• Symptoms = fever, cough, difficulty breathing
• Diagnosis = detection of cysts in lung tissue/fluid
• Treatment = trimethoprimsulfamethoxazole

20. Systemic opportunistic mycoses
Ex) Aspergillosis
• Aspergillus fumigatus
Transmission = airborne spores from soil and compost
• Most people inhale Aspergillus spores every day
• Destroyed by healthy immune systems
Pathogenesis = germinate into hyphae in alveoli  lesions
Symptoms = fever, bloody cough, chest pain
Diagnosis = lung tissue biopsy
Treatment = amphotericin B, voriconizole

21. FUNGAL PNEUMONIA
Ascomycota Sac Fungus
Aspergillus
Organism: Aspergillus fungus
Frequently found in compost heaps, air vents, pillows and airborne dust.
Transmission: Inhalation of spores is primary cause of Aspergillosis.
Course: Usually affects open spaces such as cavities that have formed in the lungs from
preexisting lung diseases.
Shows up as a tangled mass of fungus fibers, blood clots, and white blood cells. Fungus ball
gradually enlarges, destroying lung tissue, but usually doesn’t spread.
Less often can become very aggressive and rapidly spread throughout the lungs and often
through the bloodstream to the brain and kidneys (immune compromised).
Diseases of the Respiratory System

22. Opportunistic Normal Flora
Candida albicans
• Part of normal flora of mouth, skin,
intestine and vagina
• Opportunistic  candidiasis
- Oral thrush: whitish velvety sores of
the mouth and tongue
- Vaginitis (yeast infection)
Candida blastoconidia
(asexual spores) SEM
Oral thrush in an infant

23. Include Blastomycoses